A virtual memory system is one which allows addressing of very large amounts of memory, even though the main memory of the system encompasses a smaller address space. Virtual memory systems provide this capability by defining memory management units, in particular, pages or segments, have virtual memory address and corresponding physical memory addresses. A particular virtual memory address may be in main memory or in slower alternate memory, such as disk space. If a virtual address maps to a physical address of data is main memory, the information is readily accessed and utilized. If the physical address indicates that the page corresponding to the virtual address is located in the alternate memory, the page is transferred or swapped into main memory where the data can be accessed. The transfer typically necessitates that other information be swapped out of main memory back to the alternate memory to make room for the new information. This transfer is typically performed under the control of the memory management unit as either hardware or software.